Unusual excimer/dimer behaviour of a highly soluble C,N platinum(II) complex with a spiro-fluorene motif

In this work we introduce a spiro-fluorene unit into a phenylpyridine (CN) type ligand as a simple way to de-planarise the structure and increase solubility of the final platinum(II) complex. Using a spirofluorene unit, orthogonal to the main coordination plane of the complex, reduces intermolecular interactions, leading to increased solubility but without significantly affecting complex ability to form Pt···Pt dimers and excimers. This approach is highly important in the design of platinum(II) complexes, which often suffer from low solubility due to their mainly planar structure, and offers an alternative to the use of bulky alkyl groups. The non-planar structure is also beneficial for vacuum-deposition techniques as it lowers the sublimation temperature. Importantly, there are no sp3 hybridised carbon atoms in the cyclometallating ligand that contain hydrogens, the undesired feature that is associated with the low stability of the materials in OLEDs. The complex displays high solubility in toluene ~10 mg mL-1 at room temperature, which allows producing solution-processed OLEDs in a wide range of doping concentrations, 5-100% and EQE up to 5.9% with a maximum luminance of 7 400 cd m-2. Concurrently, we have also produced vacuum-deposited OLEDs, which display luminance up to 32 500 cd m-2 and maximum EQE of 11.8 %.